joshuabardwell

I'd rather try and fail than not try at all. And I don't have a Praxair anywhere near me. And I'm sure if I could get to one, it would be extremely expensive.

I haven't priced liquid hydrogen recently, but about five years ago, it was around $1.50 / gallon. Wherever you live, surely there's a local industrial gas or welding gas supplier who can sell you liquid H2. It's too much hassle to drive an hour to pick up a dewar of H2, so instead you're going to invent, from stuff you buy at the local hardware store, the apparatus to compress gaseous H2 to over 13 atmospheres of pressure? No way. Save up your pennies and buy some liquid H2 and then you can really get started on the process of figuring out how to convey the H2 to your repulsor valve without it vaporizing. You'll need hoses and valves capable of handling at least 13 atm, which is about 190 psi. Typical hydraulic hoses, such as are found on a tractor or other heavy machinery, run at over 2000 psi, which is a safety margin of at least 10x. You'll just need to figure out how to keep the H2 cold enough that it doesn't over-pressure and burst your lines. You're familiar with Boyle's law, right? You'll want to read up on that.

joshuabardwell

I don't know about hydrogen specifically, but the usual way that gasses such as propane are handled in the field is to store them in liquid form in pressurized container and then allow them to vaporize off the top and come out a valve, then handle them in gaseous form in the hoses. The regulator for a typical propane system is set around 10 psi. This means that the complex and dangerous work of handling the pressurized gas can be done in a specialized facility. The problem with trying to keep gasses in liquid state while they're in transmission lines is that the lines must either be able to handle very high pressures, or they must be insulated and/or refrigerated so as to keep the gas at a very low temperature (Boyle's Law, again). None of this is insurmountable, but the additional complexity of the refrigeration system and/or the safety issues related to handling high-pressure gasses--and most especially highly flammable gasses--means that it's just not worth it in most cases.

Why don't you spend some time researching hydrogen fuel cells being developed for cars? Ask yourself why hydrogen cars don't just use a tank of liquid H2, plumbed through high-presusre lines. Why is it that automakers have put so much work into designing hydrogen fuel cells instead?

WireJunky

Would hydrogen in gas form work though? Suppose I have a y-splitter in line with hydrogen and compressed air. A one way valve respectively on each. Is I fed compressed air into said valve with the hydrogen, would it push the hydrogen gas out at high enough speed to provide thrust?

1ChicagoDave

Would hydrogen in gas form work though? Suppose I have a y-splitter in line with hydrogen and compressed air. A one way valve respectively on each. Is I fed compressed air into said valve with the hydrogen, would it push the hydrogen gas out at high enough speed to provide thrust?

Just the gas? Or....are you planning to ignite it?

joshuabardwell

Would hydrogen in gas form work though? Suppose I have a y-splitter in line with hydrogen and compressed air. A one way valve respectively on each. Is I fed compressed air into said valve with the hydrogen, would it push the hydrogen gas out at high enough speed to provide thrust?

Please don't take this the wrong way, but this is the kind of question that indicates that you're not qualified to even take a swing at this project. I'm not an expert on hydrogen propulsion, nor am I an expert on compressed gas systems. But I am enough of a red-neck to know that when you've got a compressed gas cylinder, at over 2000 psi, you don't need to add compressed air to the line to push the other gas out. By the time hydrogen is compressed down enough that it is a liquid at room temperature, it will be MORE THAN HAPPY to come out of a valve far faster than you would like it to. That's why the compressed gas cylinder has a regulator on top.

Watch this video to see what happens when a compressed gas cylinder has its regulator knocked off: http://www.youtube.com/watch?v=ejEJGNLTo84

How's that for thrust? No additional energy needed.

Here is the one, fundamenal, insurmountable limitation in your idea to build a hand-mounted repulsor: Newton's Third Law. Assuming you can get your repulsor working, whatever force you impart on an object will be equally imparted back on you. So you will not be able to move any object larger or heavier than you could with your arms. So if you are imagining that you can harness the power of hydrogen to generate huge amounts of thrust that knock over cars and blow down walls, sorry--not going to work. If you exert enough force on a car to knock the car over, what will happen is that you will fall down and the car will stay where it was, as if the car had hit you with that amount of force instead.

WireJunky

Would hydrogen in gas form work though? Suppose I have a y-splitter in line with hydrogen and compressed air. A one way valve respectively on each. Is I fed compressed air into said valve with the hydrogen, would it push the hydrogen gas out at high enough speed to provide thrust?

Please don't take this the wrong way, but this is the kind of question that indicates that you're not qualified to even take a swing at this project. I'm not an expert on hydrogen propulsion, nor am I an expert on compressed gas systems. But I am enough of a red-neck to know that when you've got a compressed gas cylinder, at over 2000 psi, you don't need to add compressed air to the line to push the other gas out. By the time hydrogen is compressed down enough that it is a liquid at room temperature, it will be MORE THAN HAPPY to come out of a valve far faster than you would like it to. That's why the compressed gas cylinder has a regulator on top.

Watch this video to see what happens when a compressed gas cylinder has its regulator knocked off: http://www.youtube.com/watch?v=ejEJGNLTo84

How's that for thrust? No additional energy needed.

Here is the one, fundamenal, insurmountable limitation in your idea to build a hand-mounted repulsor: Newton's Third Law. Assuming you can get your repulsor working, whatever force you impart on an object will be equally imparted back on you. So you will not be able to move any object larger or heavier than you could with your arms. So if you are imagining that you can harness the power of hydrogen to generate huge amounts of thrust that knock over cars and blow down walls, sorry--not going to work. If you exert enough force on a car to knock the car over, what will happen is that you will fall down and the car will stay where it was, as if the car had hit you with that amount of force instead.

Obviously we have a miscommunication here.I am talking about a simple system, no compressed tanks or anything.

joshuabardwell

... and with that, I'm going to unsub from this thread. Good luck with your endeavor, and by "good luck," I mean, "I hope you don't somehow manage to figure out just enough of this process to seriously injure yourself."

justinhalek

I dont understand why you want to use hydrogen. In your application propane will be better/ cheaper than home made hydrogen.

2 reasons, i can buy propane cylinders for $3. you can't make the same amount of hydrogen for that cheap. Propane is very much SAFER. not safe... but safer.

Ever seen a hydrogen system suffer from a flashback? Ka-F**ing-BOOM!

EDIT: speaking from years of experience with hydrogen. You should look into propane.

Also, forget making an actual thruster.... you dont have enough money for that. if you just want the effect of a thuruster, propane will end up working better anyways.a propane a pressurized air mix will be great.

From asking all the basic questions about Hydrogen gas, it shows you know very little.NASA is the place to ask about hydrogen propulsion, but you will need a degree in rocket science first.If you do your research, you will find what you are trying to do is not new and the problems arising from it shows why we aren't all zooming around like IRON MAN.

There is a lot of talk on amateur rocketry, space enthusiast, and even "hydrogen economy" (fuel cells, etc) about how annoying hydrogen is to work with. It's ridiculously NOT dense, leaks through everything, and is a general pain in the ass. There's even substantial reasoning that using hydrogen in the Space shuttle main engines was a bad idea. About the only thing hydrogen has going for it is very good energy content per MASS, which is somewhat important for rockets. Almost ANY hydrocarbon has much better energy density per VOLUME. (russian boosters don't use hydrogen, for instance.)

Also, while you can generate hydrogen at home, it is generally very inefficient to do so. There are some jewelery torches that use electrolytically generated H2/O2 for fuel. They're apparently quite nice for welding jewelery-sized metal things, but they don't produce any appreciable thrust.

What many people new to rocketry don't realize is just how MUCH fuel has to be burnt to produce a particular thrust for a particular time...